The defence ministry was originally expected to submit an analysis of the two options by June 29 for government approval, but Pellegrini said it was too big a decision to be made under pressure.

“I want to see comparable offers to eliminate any doubts. This is a serious decision worth billions of euros,” he said.

Slovakia, a member of NATO, has a maintenance contract with Russia for its 12 MiG-29s until autumn 2019.

The contract worth 20 million to 50 million euros ($25 million to $80 million) a year, under which dozens of Russian technicians are based at a Slovak military air base, will need to be extended even after the government signs a deal to buy new jets, while it awaits delivery.

New Gripen jets would take 18 to 24 months to deliver while F-16s may take until around 2023, said Jaroslav Nad, an analyst from the Slovak Security Police Institute.

“Both options would be a step forward for Slovakia, however, there has been no public debate on whether the country needs the more expensive and more advanced F-16s or the more budget-friendly Gripens,” he added.

The ministry has not disclosed the purchase and maintenance costs of the jets.

Slovakia had been in talks with Gripen maker Saab for years, before Defence Minister Peter Gajdos, from the junior coalition nationalist and eurosceptic SNS party, paused the talks and invited other bidders. That sparked criticism from coalition partners that delays in closing the deal would prolong Slovakia’s dependence on Russia.

Saab said last month it would move a support centre from Sweden to Slovakia, which may service Gripens in service in several European countries, if it wins the deal.

Neighbouring Hungary and the Czech Republic operate Gripens. Poland flies a large fleet of 48 F-16s, built by Lockheed Martin Corp, while also keeping around 30 MiG 29s.

Bulgaria, the only other EU member state that still relies on Soviet-made MiG-29s, called for bids earlier this month to buy 16 new or used fighters to replace them.

Slovakia plans to spend about 6.5 billion euros by 2030 to modernise its military. Defence spending is due to rise from 1.2 percent of gross domestic product this year to 1.6 percent in 2020 and 2.0 percent by 2024.